Exhaust valve for a large sized two stroke diesel engine, process for reduction on nox-formation in such an engine and such engine

ABSTRACT

For reducing the NO x -emission of a large sized two stroke diesel engine having at least one combustion room ( 3 ), a reciprocating piston ( 4 ) and an exhaust opening ( 12 ) controlled by an exhaust valve ( 13 ) at each work cyclus a small volume of burnt gas is retained in the combustion room ( 3 ) and so added to the fresh air for the next combustion. For achieving this retention of burnt gas the underside of the valve disc ( 15 ) off the exhaust valve ( 13 ) is provided with a shallow concave face ( 17 ) building a basin-like collection room, whose depth is within a range of 2-10% of the outer diameter of the valve disc ( 15 ).

The invention relates according a first idea to an exhaust valve for alarge sized two stroke diesel engine, according a further idea to aprocess for reduction of NO_(x)-formation in such a large sized twostroke diesel engine, and according a still further idea to such a largesized two stroke diesel engine. Also manufacturing methods as well asuse of an inventive exhaust valve as well as of a such engine arescoped.

It is generally known in the art that peaks of combustion temperatureand herewith the generation of NO_(x) can be reduced when some burnt gasis added to the new air filling of the combustion room. For this purposeit has been proposed already to recirculate a part of the exhaust gas(DE 101 16 643 C2). But there is a risk that not only exhaust gas butalso scavenge air reaches the exhaust channel so that the exhaust gas isdiluted with scavenge air what leads to a higher oxygen content of therecirculated exhaust gas and therefor to a higher NO_(x)-formationFurther substantial disadvantages herewith are that an expensive andcomplex recirculation device is needed, and that such device isoccupying hardly-available space near the engine.

The GB 222 7055 A describes a two stroke diesel engine with an exhaustopening controlled by an exhaust valve. The underside of this exhaustvalve is concave and makes a symmetric cavity bordered by the rim. Thereason for this is here that the fuel supply tube and injection nozzleare integrated in the exhaust valve. Conserving some burnt gas in themanner of a nest within the rim area of the concave underside of theexhaust valve for reduction of NO_(x)-formation isn't mentioned. Thesame is true also for the dimension of the cavity on the underside ofthe exhaust valve.

Starting from this prior art it is an object of the invention to createan improved exhaust valve suitable for reduction of NO_(x)-formation aswell as to create an improved method for manufacturing it.

A second object of the invention is to create an improved process forreduction of NO_(x)-formation.

Further objects of the invention are to design an improved large sizedtwo stroke diesel engine as well as to create an improved method formanufacturing or remanufactoring it.

The first object is solved by the exhaust valve according claim 1 or oneof the manufacturing claims 17, 19-22 respectively.

The second object is solved by the process according claim 12.

The further objects are solved by the diesel engine according claim 23,24 or 33 respectively or one of the manufacturing claim 35 or 41respectively.

By the superposed teaching it is achieved, that the right amount ofburnt gas to add to the air for the next combustion is conserved in thecombustion room in the manner of a nest of exhaust gas built within therim area of the underside of an exhaust valve controlling an exhaustopening arranged coaxially with the combustion room. The burnt gasretained in the combustion room is not diluted with fresh air so thatthe content of oxygen is very low. Therefor just a minor volume ofretained gas is enough for an effective reduction on NO_(x)-emission aswell as for a favorable temperature distribution in the exhaust valvematerial. Further means of the said cavity the mass of the exhaust valveand therefor also the heat transfer to the gas within this combustionroom is reduced.

Useful developments and advantageous embodiments of the superposed ideasas well as manufacturing methods there of are mentioned in thesubclaims.

In the following one working example of the invention shown in thedrawing is described.

In the drawing shows:

FIG. 1 a schematic vertical section through a large sized two strokediesel engine of inventive type,

FIG. 2 schematically, the upper area of one cylinder of FIG. 1 with anopened exhaust valve according to the invention,

FIG. 3 the arrangement of FIG. 2 with closed exhaust valve and

FIG. 4 a section view along the line IV/IV in FIG. 3.

Diesel engines of the type as shown in FIG. 1 normally are used for shippropulsion or for driving big stationary power plants. Everywhere inthis description and in the related claims directional terms like up,down, side, etc. are referring to the principal relative positions ofthe piston, cylinder, combustion room, and exhaust valve as shown inFIG. 1 of a standing engine with vertical cylinder axis. At otherorientation directional terms are to be interpreted accordingly.

The diesel engine 1 shown in FIG. 1 is a large sized two stroke dieselengine of the crosshead type. For one such engine normally morecylinders are provided often as a single-row I-arrangement althoughother arrangements also are known, e.g. V-, X-, Y-arrangements. One ofthese cylinders 2 can be seen in the section view of FIG. 1. Eachcylinder 2 contains a combustion room 3 which downwards is delimited bya reciprocating piston (assembly) 4 by means of which the volume of thecombustion room can be increased/decreased.

The piston assembly 4 is connected with a crosshead assembly 5 via apiston rod 6. The crosshead assembly 5 comprises a swingable bearingconstruction of a known type, here shortly called crosshead pin 7. Thepiston rod 6 is fastened to the piston assembly and to the crossheadassembly 5. The crosshead assembly 5 is connected to a crankshaft 8 bymeans of a connecting rod 9 which has one end swingably connected at thecrosshead pin 7 and has an other end rotatably connected to a crankshaftpin as known in the art.

The cylinder 2 is provided in its lower area with air inlet slots 10.The air inlet slots 10 are opened and closed relative to the combustionchamber by the reciprocating piston 4. Through the air inlet slots 10when opened, air can be fed into the combustion room 3 for it'sscavenging and filling. Throughout this description and the relatedclaims, in this connection, “air” more than normal air from ambient alsomeans such air possibly having other gassy component(s) mixed-in to e.g.control the overall oxygen content of “air” fed into the combustionchamber. In the upper area of the cylinder 2 fuel injection valve(s) 11is/are positioned for injection of fuel into the combustion room 3 whenthe piston 4 is in the region of its top dead center.

Burning of the injected fuel is causing a downward movement of thepiston 4. After that, the burnt gas is exhausted through an exhaustopening 12 positioned at the upper end of the combustion room 3,preferably coaxially. This exhausted burnt gas normally is calledexhaust gas. The exhaust opening 12 is controlled by an assigned exhaustvalve 13. The exhaust valve 13 can be designed as a built valve or as anone piece valve. The exhaust valve can be manufactured according tovarious methods whereof some are scoped by claims. Among benefits fromsuch manufacturing methods are re-use of new possibly surplus othervalves or valve parts as well as beneficial re-use of useableparts/areas of else worn valves of compatible design. Thusmanufacture/reconditioning of an inventive exhaust valve is made moreeconomical and environmental friendly by reuse of both previous resultsof costly processing efforts and of material, then simultaneously bothleaving less waste material and requiring less virgin material. In eachcase an inventive exhaust valve has a valve shaft 14 and a valve disc 15arranged at the lower end of the valve shaft 14. In connection withlarge sized two stroke diesel engine 5 the diameter of the valve disc 15should be 100 mm at least. Also bigger diameters of for example 160-200mm or even larger would be possible. In the region of the lower end ofthe valve shaft 14 above the valve disc 15, propeller blades 16 can beprovided for rotating the exhaust valve 13 by the passing exhaust gas asis only indicated in FIG. 2, where propeller blade are shown withouttheir normal “twist”.

One 360° revolution of the crankshaft 8 wherein one full ascent and fulldescent of the piston 4 is completed defines one work cycle. During eachwork cycle a compression of the filling of the combustion room 3, aninjection of fuel, a burning of the injected fuel and the air filling ofthe combustion room 3, an opening of the exhaust valve 13 and exhaustingof burnt gas (socalled exhaust gas) as well as an opening and closing ofthe air inlet slots 10 are carried out, whereby the combustion room 3 isscavenged and filled with new air. The air inlet slots 10 might be soinclined, that the air fed into the combustion room 3 is rotated arounda central axis of the combustion room 3.

During the scavenging of the combustion room 3 some of the burnt gas isretained in the combustion room 3. This burnt gas conserved in thecombustion room 3 has a low oxygen content which causes reduction of thepeak combustion temperature and therefor reduction of the level ofgenerated NO_(x). In this way the NO_(x)-emission of the diesel engine 1can be reduced. Also the material temperature distribution in theexhaust valve and especially in it's valve disc 15 can be improved inthis way.

For this purpose the underside of the valve disc 13 is provided with ashallow rotationally symmetric concave face 17 as can be seen from FIGS.2 and 3. This rotationally symmetric concave face 17 leads to a cavity18, surroundingly bordered by the valve disc's rim area and being opentowards the combustion room 3.

The function of this cavity 18 is to build a basin-like collection roomfor retention of burnt gas when the exhaust valve 13 is opened as isschematically shown in FIG. 2. During the compression stroke of thepiston 4 the collected and retained burnt gas can build up a nest 19 ofburnt gas on the underside of the exhaust valve 13. The upper side ofthe piston 4 is in this example provided with a rotationally concaveface 20 opposite to the concave underside of the exhaust valve 13. Thisassist the nest formation mentioned above as can be recognized from FIG.3. Of course a flat piston top surface can be used under circumstances.

During activation of the fuel injection valves 11 the fuel at leastpartly is injected in the nest 19 of burnt gas conserved in thecombustion room 3 as is indicated by spraying lines 21 in FIGS. 3 and 4.The spray direction is inclined against the radial direction so thatmost of the fuel is injected into the fresh air rotating according arrow22 in FIG. 4 and a small part hits the nest 19 of retained burnt gas.Since this burnt gas has a low oxygen content the combustion is retardedand therefor peaks of combustion temperature and NO_(x)-formation arereduced.

The concave face 17 of the underside of the exhaust valve 13 is sodesigned that the maximum of the rise relative to an imaginary directlysupporting planar face 23, indicated in FIG. 2, is within the range of2% to 10% of the outer diameter of the valve disc 15, which can be 100mm-160 mm or bigger as mentioned above. Preferably this range can be5%-7% and highly preferably 6%-6.5% of the outer diameter of the valvedisc 15. This dimensioning of the rise of the concave face 17 results ina sufficient volume of conserved burnt gas. The basin-like cavity 18 canfurther be so designed that it's volume is within the range of 0.5%-3%of the volume of the combustion room 3 in it's mostly diminishedcondition, that is when the piston 4 has reached it's top deadcenter—the exhaust valve 13 of course at the same time being fullyraised to seal the combustion room 3 towards the exhaust opening 12.Preferably this range can be 1%-2% and highly preferable 1.6%-1.7% ofthe said minimum volume of the combustion room 3.

Said volume of the cavity 18 would lead to an enlargement of the totalvolume of the combustion room 3. For avoiding such enlargement,compensation means are provided. For achieving the wished compensationthe top level of the piston 4 can be raised accordingly compared to anarrangement with an uncarved exhaust valve. This can be done byproviding the upper face (part) of the piston 4 with a top layer ofcorresponding thickness. According an other possibility which is toprefer a shims layer of corresponding thickness can be inserted betweentwo supporting areas assigned to the piston assembly 4. In the preferredembodiment shown in FIG. 1 a shims layer 24 is shown inserted betweenmutually supporting areas of the piston rod 6 and of the crosshead pin7, respectively.

Manufacturing of a large sized two stroke diesel engine scoped by theinvention generally is performed by mounting of at least one inventiveexhaust valve to any other part or assembly of parts being/to be part ofa said engine. The latter method is highly relevant as submounting tomajor assemblies before final assembling of the engine is very commonfor this size of engines often used as sole source for propulsion powerin a ship. Also mounting of a shims layer between two supporting areasassigned to a piston assembly being/to be delimiting a combustion roomalso being/to be delimited by an inventive exhaust valve can becomprised in such manufacturing. Preferably during the manufacturing ashims layer is inserted between a present crosshead pin structure andit's corresponding piston rod to co-function at same combustion roomwith an inventive exhaust valve.

In most cases a new large sized two stroke diesel engine is built by themanufacturing, but a used such engine can be brought to a scoped stateby retrofitment to an existing large sized two stroke diesel engine ofelse known type, of at least one inventive exhaust valve to replace aconventional exhaust valve which of course previously was removed fromsaid engine. Preferably inventive exhaust valves then are installed forall the engine's cylinders, that an else for environmental reasons“forbidden”/“dead” engine cheaply can be “revived”, possibly as anoriginal-MAN B&W-brand-“refurbished” engine, to yield many more years ofeffective service e.g. when installed in a ship then being acceptable tothe current IMO-rules. (IMO=International Maritime Organization, aUnited Nations body issuing maritime regulations, “TIER”s, for emissionsupper limits, etc.)

A special type of retrofitment or remanufacturing occurs when at anexisting large sized two stroke diesel engine already having inventiveexhaust valves mounted, one or more of these exhaust valves are replacedby an other inventive exhaust valve having a shape of it's valve headbeing different from the replaced exhaust valve. The purpose of suchreplacement then is to obtain a better reduction of theNO_(x)-formation. Reasons herefor can be shift to use of other fuel fora time period of substantial length, that a new optimization is requiredfor an engine mounted in a ship, that this ship still can fulfil e.g.IMO-requirements to low emissions to get access to coastal areas and thehaurbours lying there. Such retrofit also can be relevant when saidengine, maybe still with same fuel-type, for a period of time isforeseen to function at a typical power output level deviating more than15% from a recently used other typical power output level, e.g. becausea raised level of fuel prizes makes it beneficial to reduce the nominalcruising speed from e.g. 90% of max. engine power to say 60% of the max.engine power, often resulting in only a few knots reduced sailing speed.Remanufacturing of an inventive large sized two stroke diesel engine byreplacement of a worn exhaust valve with an inventive exhaust valve isanother beneficial posibility of manufacture of a such large dieselengine yielding a possibility to revitalize an else worn out engine.

For all such engine manufacturing it is foreseenable to use inventiveexhaust valves provided by any mentioned or claimed method ofmanufacturing of inventive exhaust valves. Common to all such methodsare processing to an exhaust valve from a specific state. Suchprocessing of course is to be understood in a broad sense and cantherefore comprise e.g. milling, turning, grinding, polishing or othermaterial removal methods, but also material combining, adding orcompacting methods as welding, depositing methods like sintering,metalspraying, pressing, forging etc. or known combinations thereof, allof which methods are well known to the person skilled in the art.

Further, an inventive exhaust valve embodiment of a given external discdiameter may be manufactured in a number of almost similar variantswhich are very difficult to effectively destinguish/identify by simplehuman visual observation of the shape of the cavity in the valve'sunderside, or by a simple measuring procedure. Thus a pronounced riskhas been reported, for faulty selection of a thus unsuited inventiveexhaust valve for later being mounted to function in an inventive largesized two stroke diesel engine. Consequently said engine afterwards withsuch faulty selected and installed inventive exhaust valve willmalfunction, possibly to a degree that access to some “restrictedpollution” coastal/harbour zones may be denied for the vessel which ispropelled by the malfunctioning engine. Therefore, and due to thepossibly large amount of details required to fully document an inventiveexaust valve, such valve preferably is made easily identifiable by datastored at various occasions to contactlessly be read from at least onetag of said valve, preferably a tag of a RFID-type, comprising storeddata to unambiguously define said valve.

Preferably at least one tag is further loaded with data specifyingdetails to authenticate said valve, such authenticating data preferablyalso comprising manufacturing-, (IMO-)approval-, historic and possibleor planned future use-data for said valve.

Preferably at least one said tag is located within the ¾ of the valveoverall axial length opposed the valve disc end. Hereby is secured thatat least this tag, normally being an electronic device sensitive to hightemperatures, can be given a position shielded from being swept anddestroyed by the very hot exhaust gas leaving the combustion chamber,when the exhaust valve is opened. Instead then the tag of said exhaustvalve can be exposed for reading by non-contacting means positionedabove the combustion room for said exhaust valve.

Normally such reading is performed before/at engine startup to supplyparameters/data to the engine's control system, but reading of a suchtag by non-contacting means to collect data from the at least one suchsaid exhaust valve can also be performed during the functioning of aninventive large sized diesel engine. Hereby a person who could be aninspector from IMO or a ship insurance company, could verify theinstalled exhaust valve to allow continued function of the engine, datafor such accept possibly also being read into the tag at the same time,without for this purpose having to stop the engine.

In the description above preferred embodiments of the invention areexplained. But the invention is not restricted to this. The protectedscope of the invention is specified in the following claims.

1. Exhaust valve designed for controlling an exhaust opening (12) of alarge sized diesel engine of the two stroke type and having a valve disc(15) arranged at the lower end of a valve shaft (14), whereby the valvedisc's (15) underside to face a combustion room (3) is provided with abasin designed as a rotationally symmetric cavity (18), beingsurroundingly bordered and being downwardly open, characterized in thatfor retention of burnt gas, the maximum of rise of the concavely shapedunderside of the valve disc (15) relative to an imaginary planar face(23) directly supporting the valve disc (15), is within the range of2-10% of the outer diameter of the valve disc (15).
 2. Exhaust valveaccording claim 1, characterized in that the maximum of rise of theconcavely shaped underside of the valve disc (15) relative to animaginary planar face (23) directly supporting the valve disc (15) iswithin the range of 5-7% of the outer diameter of the valve disc (15).3. Exhaust valve according claim 2, characterized in that the maximum ofrise of the concavely shaped underside of the valve disc (15) relativeto an imaginary planar face (23) directly supporting the valve disc(15), is within the range of 6-6.5% of the outer diameter of valve disc(15).
 4. Exhaust valve according claim 1 or 2, characterized in that theouter diameter of the valve disc (15) of the exhaust valve (13) is atleast 100 mm.
 5. Exhaust valve according claim 4, characterized in thatthe outer diameter of the valve disc (15) of the exhaust valve (13) isat least 160 mm.
 6. Exhaust valve according claim 1 or 2, characterizedin that the valve disc (15) having the cavity (18) designed as the basinfor retention of burnt gas is provided with a protection layer on thevalve disc's underside.
 7. Exhaust valve according claim 1 or 2,characterized in that it is designed as a built valve whereby the valvedisc (15) is applied to the valve shaft (14).
 8. Exhaust valve accordingclaim 1 or 2, characterized in that the valve shaft (14) is providedwith propeller blades (16).
 9. Exhaust valve according to one or more ofprevious claims, characterized in being identifiable by datacontactlessly read from at least one tag of said valve, preferably a tagof a RFID-type, comprising stored data to unambiguously define saidvalve.
 10. Exhaust valve according to claim 9, characterized in at leastone said tag being further loaded with data specifying details toauthenticate said valve, such authenticating data preferably alsocomprising manufacturing-, approval-, historic and possible or plannedfuture use-data for said valve.
 11. Exhaust valve according to claim 9or claim 10, characterized in at least one said tag being located withinthe ¾ of the valve overall axial length opposed the valve disc end. 12.Process for reduction of the NO_(x)-formation in a large sized dieselengine (1) of the two stroke type having at least one combustion room(3) with an exhaust opening (12) coaxially arranged within andcontrolled by an exhaust valve (13) which is realized according any ofthe foregoing claims, whereby in the combustion room (3) at each workcycle a fuel injection, a combustion of fuel, an ejection of burnt gas,a scavenging and filling with fresh air as well as a compression of thefilling of the combustion room (3) are carried out, whereby some burntgas is added to the air before combustion, and whereby at least some ofthe burnt gas added to the air is conserved in the combustion room (3)in the manner of a nest (19) of burnt gas built within the rim area ofthe underside of the said exhaust valve (13) being concavely shaped onthe underside.
 13. Process according claim 12, characterized in that thefresh air fed to the combustion room (3) is rotated around a centralaxis.
 14. Process according claim 12 or 13, characterized in that atfuel injection the fuel at least partly is injected from outward of thenest (19) into the nest (19) of burnt gas built on the underside of theexhaust valve (3).
 15. Process according claim 12 or 13, characterizedin that the exhaust valve (3) is rotated around it's axis, during timewhen not being in a fully closed position.
 16. Process according claim12 or 13, characterized in that most of the fuel is injected into thefresh air.
 17. Manufacturing of an exhaust valve according to one ormore of the claims 1-11, characterized in said valve being made as a newsaid valve from new elements.
 18. Manufacturing of an exhaust valveaccording to claim 17, characterized in said exhaust valve initially wasmade and identified as a finished new exhaust valve not comprising thecharacterizing feature of claim 1, and said finished new exhaust valveafterwards is further processed to obtain a state being scoped by one ormore of the claims 1-11.
 19. Manufacturing of an exhaust valve accordingto one or more of the claims 1-11, characterized in said valve beingmade by further processing of a used valve not hitherto having comprisedthe characterizing feature of claim 1, to obtain a state being scoped byone or more of the claims 1-11.
 20. Manufacturing of an exhaust valveaccording to one or more of the claims 1-11, characterized in said valvebeing made by reconditioning of a worn exhaust valve at least earlier(possibly still) having comprised the characterizing feature of claim 1,to obtain a functional state being scoped by one or more of the claims1-11.
 21. Manufacturing of an exhaust valve according to one or more ofthe claims 1-11, characterized in said valve being made by specialprocessing of an existing exhaust valve, such special processingcomprising the steps of: removal of a valve shaft part area from theresidual valve disc part area, and attachment of an other valve shaftpart area to the residual valve disc part area, the resulted exhaustvalve then comprising the residual valve disc part area, to obtain astate being scoped by one or more of the claims 1-11.
 22. Manufacturingof an exhaust valve according to one or more of the claims 1-11,characterized in said valve being made by special processing of anexisting exhaust valve, such special processing comprising the steps of:removal of a valve disc part area from the residual valve shaft partarea, and attachment of an other valve disc part area to the residualvalve shaft part area, the resulted exhaust valve then comprising theresidual valve shaft part area, to obtain a state being scoped by one ormore of the claims 1-11.
 23. Large sized diesel engine of the two stroketype having a combustion room (3) delimited by a reciprocating piston(4), characterized in having at least one exhaust valve (13) accordingany of the foregoing claims 1-11.
 24. Large sized diesel engine of thetwo stroke type having a combustion room (3) delimited by areciprocating piston (4), characterized in having at least one exhaustvalve according to claim 11, and the tag of said exhaust valve beingexposed for reading by non-contacting means positioned above thecombustion room for said exhaust valve.
 25. Large sized diesel engineaccording to claim 24, characterized in that the else added combustionroom (3) volume caused by the cavity (18) on the underside of the valvedisc (15) is compensated by raising the top face level of the piston(4), compared to an arrangement with an uncarved valve disc.
 26. Largesized two stroke diesel engine according claim 25, characterized in thata shims layer (24) is provided between two supporting areas assigned tothe piston assembly (4), for a compensating elevation of the piston topface.
 27. Large sized two stroke diesel engine according claim 25 havinga crosshead (5), the pin of which is connected with the piston assembly(4) via a piston rod (6) supported on the crosshead (5) construction,characterized in that a shims layer (24) is inserted between thecrosshead pin (7) and the piston rod (6).
 28. Large sized diesel engineaccording to claim 24 or 25, characterized in that the volume of thecavity (18) on the underside of the valve disc (15) is within the rangeof 0.5-3.0% of the volume of the combustion room (3) when the exhaustvalve is in closing position and the piston (4) has reached the top deadcenter.
 29. Large sized diesel engine according claim 28, characterizedin that the volume of the cavity (18) on the underside of the valve disc(15) is within the range of 1-2% of the volume of the combustion room(3) when the exhaust valve is in closing position and the piston (4) hasreached the top dead center.
 30. Large sized diesel engine accordingclaim 29, characterized in that the volume of the cavity (18) in theunderside of the valve disc (15) is within the range of 1.6%-1.7% of thevolume of the combustion room (3) when the exhaust valve is in closingposition and the piston (4) has reached the top dead center.
 31. Largesized diesel engine according claim 24 or 25, characterized in that thepiston (4) has a concave upper side (20) opposite to the concaveunderside (17) of the exhaust valve (13).
 32. Large sized diesel engineaccording claim 24 or 25, characterized in that in the combustion room(3) fuel injection valves (11) are located out of the concave underside(17) of the exhaust valve (13).
 33. Large sized diesel engine of the twostroke type, characterized in having the combustion room (3) of at leastone of it's cylinders operated by a process according claim
 12. 34.Large sized diesel engine of the two stroke type according to claim 33,characterized in to at least one said cylinder's combustion room havingmounted an exhaust valve according to claim 11, and the tag of at leastone such said exhaust valve during functioning of said large sizeddiesel engine is read by non-contacting means to collect data from thetag.
 35. Manufacturing of a large sized two stroke diesel engine toaccord to one or more of the claims 23 to 34, characterized in mountingof at least one exhaust valve according to one or more respectivelyrelevant of the claims 1 to 11, to any other part or assembly of partsbeing/to be part of a said large sized two stroke diesel engineaccording to one or more of the claims 23 to
 34. 36. Manufacturing of alarge sized two stroke diesel engine according to claim 35,characterized in mounting of at least one shims layer between twosupporting areas assigned to a piston assembly being/to be delimiting acombustion room also being/to be delimited by an exhaust valve accordingto one more of the claims 1 to
 11. 37. Manufacturing of a large sizedtwo stroke diesel engine according to claim 35 or 36, characterized ininsertion of a shims layer between a present crosshead pin structure andit's corresponding piston rod to co-function at same combustion roomwith an exhaust valve according to one more of the claims 1 to
 11. 38.Manufacturing of a large sized two stroke diesel engine according to oneor more of the claims 35 to 37, characterized in said large sized twostroke diesel engine is built as a new engine.
 39. Manufacturing of alarge sized two stroke diesel engine according to one or more of theclaims 35 to 37, characterized in retrofitting to an existing largesized two stroke diesel engine not being scoped by any previous claim,of at least one exhaust valve according to one or more of claims 1 to11, to replace an exhaust valve not scoped by any present claim, whichlatter valve previously was removed from said engine.
 40. Manufacturingof a large sized two stroke diesel engine according to one or more ofthe claims 35 to 39, characterized in at an existing large sized twostroke diesel engine being scoped by one or more previous claims,replacing at least one exhaust valve according to one or more of claims1 to 11, with an other exhaust valve according to one or more of claims1 to 11 but having a shape of it's valve head being different from theexhaust valve to replace, to better reduce the NO_(x)-formation,preferably when said engine for a period of time is foreseen to functionat a typical power output level deviating more than 15% from a recentlyused other typical power output level.
 41. Remanufacturing of a largesized two stroke diesel engine according to one or more of the previousclaims, characterized in replacement of a worn exhaust valve with anexhaust valve according to one or more of the claims 1-11.